During a harmful algal bloom and associated mass fish mortality event in 2025/26, hundreds of rare and cryptic fishes were found along the shores of Gulf St Vincent in South Australia. This unprecedented event presented a unique opportunity to collect and study fresh specimens of several species that could never have been targeted to sample in such high numbers and for which biological knowledge remains limited. Collected taxa included prowfishes, anglerfishes, seaperches, and southern blue devil. Specimens were processed to obtain genetic voucher material, establish museum voucher specimens and generate data on morphometrics, sex, and otolith ages. The data analyses provided novel insights into the biology and life history of a range of rare and cryptic fishes that were previously poorly understood. The findings expand baseline knowledge of several species and offer valuable information to assess population resilience following large-scale mortality events. This improved understanding can inform predictions of natural population recovery trajectories, management actions and possible recovery interventions.